As there becomes more interest and activity in direct broadcast satellite transmission systems, by which signals may be received at a receiving dish at each subscriber's home, and especially where some of those signals may be high-priority signals such as for pay TV television channels and the like, the problem of scrambling those signals so as to avoid access to them except to subscribers who have the right to such access, becomes more severe. In some respects, cable operating systems also have the same problems, in that many data streams or television programs or the like may be transmitted throughout a cable system, where perhaps only some of the subscribers have the right of access to certain of the program material.
The same problems, and thus the same general solutions, may also be related to other forms of data stream transmission and reception, such as conferencing data (video and/or audio) from remote locations, and the transmission of data having commercial or military security requirements from remote locations and/or over long distances.
DBS operating systems are generally intended for operation at a nominal frequency of 12 gHz, where a plurality of differing source material is transmitted from a common transmitter to a satellite and thence is beamed downwardly to a reception area which may, indeed, cover many thousands of square kilometers. Other transmission systems operate off stationary satellites at lower frequencies, generally 4 gHz, and still other multi-channel broadcasting systems are cable-related, where there may be no free air transmission. In any event, whenever the data is transmitted in a frame-by-frame manner, such as television signals or other secure data, there is a requirement that synchronizing information be transmitted with the various data streams so that the receiving tuners and demodulators may lock onto the signal without video roll-over, or the like. However, when there is a desire to isolate one or more of a plurality of data streams, such as pay tv program material, high security data, or the like, from reception other than by authorized receivers or subscribers, it is the usual approach to "scramble" those signals such as by moving the signals or data streams from channel to channel on a regular or irregular basis, thereby requiring that the tuner at the recieving end of the broadcast also moves from channel to channel in order to continue to track the program material or data stream. This, however, may create difficulties in that synchronization may be lost each time the channel upon which the data stream is being transmitted switches to another channel, so that one or more frames of data may be lost at the receiver before re-synchronization is achieved. This may occur because of the inability of the local oscillator in the tuner to be able to shift frequencies sufficiently fast so as to be able to lock onto the next designated channel frequency within the interval between frames, so that one or several frames of data may be lost.
Moreover, where there may be several data streams of differing information that are to be scrambled, it may also happen that each of those data streams may have differing priority levels. For example, in a system that provides access to certain television programs to subscribers who pay the necessary fees, there may be a first priority by which subscribers would have access to television transmissions of first-run movies, a second priority where subscribers would have access to live sporting events such as boxing matches or international team events or the like, and a third priority permitting access to "adult" movies or the like. All of those priorities may be mutually exclusive to one another, or they may be graded so that access to priority three permits access to priorities one and two as well, but access to priority one precludes access to the other two priorities, and so on.
In any event, it may be that in a DBS system, or a cable system, all or at least some of the data streams or program channels may be scrambled, whereby access to the scrambled channels can be achieved only by having access to the unscrambling data so as to achieve any meaningful reception. Access to certain priority channels may be otherwise denied except upon possession by the subscriber of the necessary additional access keys. Of course, all such access codes and keys, etc., are or may be embedded electronically as digital or analog data within the data stream.
There thus becomes the requirement that the tuner and data stream access hardware installed at each subscriber's home, or otherwise, must have the ability to detect the necessary routing by which the scrambling has occurred, so as to unscramble the transmitted channels and therefore so as to be able to track a given program or data stream. Of course, such hardware must be such as to be able to switch from one assigned channel frequency to another, according to the routing code, as quickly as possible to avoid loss of synchronization or lock-out, and in the worst case condition within the time required for transmission and reception of one frame of data.
This also means that competing DBS and/or cable systems may operate, each having their own scrambling and descrambling protocols, where a subscriber to one system would be unable to receive and unscramble program material from the other system. It becomes even more apparent when it is recognized that data packages carrying all of the routing and identifier codes may by encrypted in the data streams.
What is meant by "encryption" is that a program material or data package is "buried" at some place within the data stream signal, by codification of the data but not codification of the signal stream itself. That is, encryption of routing data within a package can occur by first generating an encryption key code, by which even if the data is read it may not be decrypted without access to the encryption key so as to make the routing code meaningful. Examples of encryption, and routing, will be discussed hereafter.
Several prior patents have been noted, which teach varying approaches to scrambling and descrambling of data, and in all of those instances the data is specifically related to television broadcast program material. For example, KIRK, Jr. et al, U.S. Pat. No. 3,733,431, issued May 15, 1973, teaches an apparatus which is particulary for use in CATV systems, whereby only subscribers who have paid an extra premium may obtain access to certain of the television programs being transmitted. The patent speaks of "encripted" signal distribution, but the technique described is one of simple scrambling between predetermined transmission channels at a relatively low but preferrably non periodic rate.
HARNEY, U.S. Pat. No. 3,789,131, issued Jan. 29, 1974, teaches a coding system for subscription television, where once again a television signal is switched between channels and where an enabling signal is transmitted to each subscriber so that, after the cannels have been switched, each of the selected subscribers who have paid the necessary premium may have access to the new chanel. HARNEY specifically requires that the channel switching commands be sent during the vertical blanking interval of the television program material to be switched, where first there is an initial authorization cycle which preceeds the start of a coded program. Because all subscribers who have paid the premium are first enabled by the initial authorization cycle, the actual channel switching command does not contain an address of any subscriber, and need not be repetitive, so that it may be sent during the vertical blanking interval between frames of the television program which is being coded for authorized reception only.
FORBES, U.S. Pat. No. 3,914,534, issued Oct. 21, 1975, teaches yet another method and apparatus for scrambling and unscrambling premium television channels, whereby a scrambling code is generated and sent to selected subscribers whereby they may unscramble the premium program. The scrambling occurs by switching from one to another video channel during the vertical interval, and is made more secure by transmitting a second program signal in field synchronization with the premium program signal, and so that after switching, more efficient use is made of the existing communication channels.
It is an advantage of the present invention that, especially in a DBS operating system, transponder operating frequencies may be assigned to the convenience of the overall system, rather than having to conform to existing transponder allocation frequencies. Indeed, the same may be said for cable operating systems. Thus, additional channels or subcarriers may be included in the same frequency spectrum, because the present invention provides means for accurately tracking any given data stream as it moves among various assigned channel or transponder frequencies.
We have discovered that by synchronizing a plurality of data streams, each of which has discrete and recognizable synchronizing information, and where there are at least as many signal channels as there are data streams, the data streams may be scrambled and unscrambled in a very secure manner by imposing an encryption key code onto each of the data streams and encrypting a data package which contains an identifier code for each data stream and a routing code by which the plurality of data streams is to be routed, in each data stream, so that the plurality of data streams may be scrambled by assigning each of them to a specific channel at any given instant of time. Moreover. the scrambled channels may be received and, by capturing the encryption key code and utilizing it to decrypt the encrypted data package so as to decode the identifier and routing codes, they may be descrambled in order that any given data stream may be tracked, no matter on which transmitted channel it may appear at any instant of time.
Each of the data streams may have a plurality of identifiable data stream categories which may or may not be mutually exclusive in any combination. Access may be permissible to any designated data stream category or combination of categories, according to the present invention, by the provision of an access data key; where the encrypted data package in a data stream may include, periodically or aperiodically, coded data stream category access data which is relevant to the category of the respective data stream being transmitted at that time. Of course, the present invention particulary envisages that at least one or more, if not all, of the data streams will have a video signal and other data present. That other data may comprise mono or stereo audio signals, conferencing data or other proprietary data by which at least two remote locations are joined together for a multi-path exchange of data, to which limited access is desirable.
It is a particular feature of the present invention that, for the fastest and most efficient operation, each authorized reciever is equipped with a microprocessor which has memory, and where a common encryption algorithm is written into the memory of each of the microprocessors at each authorized receiver. Moreover, each authorized receiver would, in the most common mode by which the present invention may be practiced, have a unique address.
The present invention provides two general approaches to the problem of controlling a local oscillator (voltage controlled oscillator) so as to effectively track a given data stream as it is switched among the assigned signal channel frequencies. Control of the voltage controlled oscillator may be by way of a phase lock loop frequency synthesizer acting together with a digital to analog converter, whereby switching of the local oscillator frequency may be very fast because substantially the correct voltage is imposed upon it. Alternatively, the output of the voltage controlled oscillator may be directly controlled by a digital to analog converter whose output is continuously updated by reference to the amount of drift that there may be by the oscillator from the actual frequency which is intended, where the drift may occur as a consequence of changing temperature or other environmental conditions and occurs relativey slowly.
It is a purpose of the present invention to provide methods of scrambling and unscrambling a plurality of data streams using encryption and decryption of data packages within the data streams, whereby any given one of the data streams may be tracked no matter on what signal channel it may appear at any instant of time.
A further object of the present invention is to provide limited acbess by authorized subscribers only to certain permium data channels having specific data categories.
Yet a further object of the present invention is to provide methods of controlling a voltage controlled local oscillator so that tracking of a given data stream may be effected without loss of data, assuming that the data is transmitted in a frame-by-frame manner and that tracking of the data stream from one assigned signal channel to another occurs by following the data stream as it is switched during the interval between successive frames of data.
Moreover, the present invention provides apparatus for scrambling and descrambling data streams, with several alternative embodiments of apparatus for controlling the output of a local oscillator so as to effect data stream tracking as it is switched among the assigned signal channels.